Integrated circuits are used in a variety of electronics applications, including communications systems, microprocessors, and other systems. Often, integrated circuits will include electrically conductive traces referred to as “transmission lines” that may carry synchronization signals (e.g., clock signals, oscillator signals, etc.) or other signals over long distances, in some cases throughout an entire integrated circuit. These transmission lines are often susceptible to noise from other adjacent circuitries and/or interconnects on the integrated circuit and/or off the integrated circuit. Such noise can lead to numerous undesirable effects, including signal demodulation, crosstalk, spurs, and/or other effects.
To reduce the incident of noise, integrated circuit designers often employ a technique known as electromagnetic shielding, or simply “shielding.” Shielding is a process by which electromagnetic field in a space may be reduced by blocking the electromagnetic field with barriers made of conductive or magnetic materials. Thus, by shielding transmission lines, such transmission lines may be electromagnetic isolated from the environment through which the transmission lines run.
FIGS. 1A and 1B depict traditional approaches to shielding differential transmission lines in integrated circuits. As shown in FIG. 1A, one traditional approach to shielding transmission lines in an integrated circuit is to include one or more conductive traces 104 parallel to the transmission lines 102, typically formed in the same metal layer as the transmission lines, and often typically coupled to a high-electrical potential or low-electrical potential (e.g., a voltage source or ground voltage). As shown in FIG. 1B, another traditional approach includes forming one or more “planes” 106 of conductive material running parallel to the metal layer of the integrated circuit from which the transmission lines 102 are formed, wherein such planes are often typically coupled to a high-electrical potential or low-electrical potential (e.g., a voltage source or ground voltage). In some instances, the approaches depicted in FIGS. 1A and 1B are combined. However, such traditional approaches have disadvantages. For example, while the approach used in FIG. 1A often provides effective shielding for lateral sources of noise (e.g., in same plane as the differential transmission lines), other sources of noise are not effectively shielded. The approach in FIG. 1B provides more effective shielding (especially when coupled with the approach in FIG. 1A), but leads to a relatively high current drain in the differential transmission lines, thus leading to greater power consumption.